If you want to be conservative about your data, it looks like Datomic is an excellent choice. It preserves the entire history of your data instead of allowing it to be modified in place.
Disclaimer: I'm a huge fan of clojure and Hickey and I think Datomic sounds amazing. I'm currently looking for an excuse to play with Datomic and learn more about it, so don't take what I said as any indication that I'm somehow against Datomic.